(a) Field of the Invention
The present invention relates to thermoplastic wholly aromatic copolyimide esters having excellent dimensional stability and to processes for producing the same. More particularly, the present invention relates to novel thermoplastic wholly aromatic copolyimide esters and processes for producing the same which may be suitably used for electric or electronic parts, etc., which require heat resistance and excellent dimensional precision and dimensional accuracy in both flow direction (machine direction: MD) and a direction making a right angle with the flow direction (transverse direction: TD).
(b) Description of the Related Art
In recent years, thermoplastic resins having extremely small coefficients of linear expansion in MD have come to be known. These resins are a series of resins called thermotropic liquid-crystalline polymers, and some examples of such resins are the wholly aromatic copolyesters disclosed in Japanese Patent Application Laid-open No. 54-77691.
Although these polyesters have small coefficients of linear expansion in MD, they are yet unsatisfactory in dimensional stability because their coefficients of linear expansion in TD are much the same as those of common thermoplastic resins.
Also, polyimide esters containing both imide bonds and ester bonds in their polymer molecules have been well known. For example, those having excellent, heat resistance are disclosed in U.S. Pat. No. 3,542,731, those improved in heat resistance, mechanical properties, and processability in Japanese Patent Application Laid-open No. 58-67725, those having high moduluses of elasticity in Japanese Patent Application Laid-open No. 55-84326, those having high toughness in Japanese Patent Application Laid-open No. 58-113222, and those having high rigidity in Japanese Patent Application Laid-open No. 60-4531. However, these polyimide esters are also hardly satisfactory in dimensional stability.